(a) Field of the Invention
A positive active material for a lithium secondary battery and a method of preparing the same are disclosed.
(b) Description of the Related Art
As use of small portable electric/electronic devices has widely increased, a new secondary battery such as a nickel hydrogen battery or a lithium secondary battery has been actively developed. The lithium secondary battery uses carbon such as graphite and the like as a negative active material, a metal oxide including lithium as a positive active material, and a non-aqueous solvent as an electrolyte solution. The lithium is a metal having a high ionization tendency and may realize a high voltage, and thus is used to develop a battery having high energy density.
The positive active material to be used for the battery is a lithium transition metal oxide including lithium as a positive active material, and specifically, 90% or more use a layered lithium transition metal oxide such as cobalt-based and nickel-based lithium transition metal oxides, a three component-based lithium transition metal oxide in which cobalt, nickel, and manganese coexist, and the like.
However, the layered lithium transition metal oxide that is widely used as a conventional positive active material has reversible capacity of less than or equal to 200 mAh/g−1 and thus has a limit in terms of energy density. In order to solve the problem of the conventional layered lithium metal oxide, a lithium-rich lithium metal oxide positive active material having 1 or more lithium compounds has been actively researched.
Accordingly, in order to solve the problem of a lithium secondary battery due to the limited reversible capacity of a positive electrode, a lithium-rich lithium metal oxide (OLO) positive active material has been suggested instead of the layered lithium transition metal oxide.
The lithium-rich lithium metal oxide positive active material includes a conventional layered positive electrode material which is combined with a Li2MnO3 phase, and may realize high capacity of greater than or equal to 200 mAh/g−1 since the Li2MnO3 phase is electrochemically activated into a layered lithium transition metal oxide through a reaction of oxygen dissociation, lithium extraction, and the like when initially charged at 4.6 V or more.
However, since this lithium-rich lithium metal oxide positive active material is difficult to uniformly prepare during preparation of its precursor, its particle density may be deteriorated or its composition depending on a depth may not be uniform, and thus its electrochemical activation through a high voltage charge is limited, the positive active material has deteriorated discharge capacity, and in addition, since manganese (Mn) elution becomes severe at a high temperature and a high voltage, performance and cycle-life characteristics of a battery may be deteriorated.
Accordingly, in order to prepare a lithium-rich lithium metal oxide positive active material having excellent charge and discharge characteristics and cycle-life characteristics as well as high capacity, a method capable of decreasing a manufacturing cost and time as well as easily adjusting a particle size and a surface porosity has been required.